1. Field of the Invention
This invention relates to a new and improved hermetically sealed container for semiconductor and other electronic devices. More particularly, this invention relates to such a container designed and intended to hermetically seal electronic devices, such as semiconductor integrated circuit devices and the like. This invention also relates to a novel sealing cover for use in fabricating the above referenced hermetically sealed container, and to a novel process for manufacturing said container and cover.
2. Prior Art
The majority of semiconductor integrated circuit devices are housed in hermetically sealed packages commonly referred to as dual-in-line, flatpack, and hybrid packages. Several designs of such packages are now in use. Among these is one which consists of a ceramic base, a cover, a lead frame, and solder glass for sealing the frame between the base and the cover, known in the trade as the CERDIP (Trademark) package. Another package type consists of a lead frame sandwiched between layers of a glass-ceramic mixture. A cavity is left in one of the layers and the semiconductor device is sealed into the cavity with a metal lid and solder preform. Premolded and transfer-molded plastic packages are also used. One popular type of package is made from a single layer of ceramic having a screened, conductive lead frame pattern deposited on it, the terminal pins on the side of the package being brazed on to give a so-called "side braze" package. This type of package is also made with two layers of ceramic material with the screened conductive pattern sandwiched between the layers and ordinarily sealed with metal lids and metallic solder preforms. A number of packages comprising hybrids of those described above are also in use.
An especially effective hermetically sealed container for electronic devices is described and claimed in U.S. Pat. No. 4,105,861. The container of this patent comprises a supporting pad for an electronic device, a conductive lead frame surrounding the pad and forming therewith a unitary construction, and a sheet of homogeneous epoxy resin extending over and fused to each face of the frame and its conductive leads, at least one of the sheets having an aperture dimensioned and disposed to surround the supporting pad and a portion of the adjacent leads of the lead frame. The container further comprises upper and lower cover plates of a material of the group comprising metal, ceramic, glass, and rigid plastic fused to the plastic sheets, one of such plates having an opening in registry with the aperture in the adjacent one of the plastic sheets for receiving an electronic device to be supported on the pad. The container further comprises means for hermetically sealing the opening in such one of the cover plates as for example a gold plated KOVAR.RTM. lid with a gold-tin eutectic solder perform.
In an alternative construction, the supporting pad for the electronic device is a portion of the lower cover plate in the form of an upwardly-protruding pedestal and each of the plastic sheets has an aperture dimensioned and disposed to surround such supporting pad and a portion of the adjacent leads of the lead frame, the pedestal extending at least partially through the aperture of the adjacent one of the plastic sheets.
While all of the above-described packages are relative effective, they suffer from some inherent disadvantages. The most pervasive disadvantage is the expense of the container because of the high price of gold, and gold price volatility. For example, the thickness of the gold plating on the KOVAR.RTM. cover lid is specified as a minimum thickness, typically fifty micrometers. Many millions of these lids are produced each year, and the cost of the gold used in plating the lids is several millions of dollars.
Thus, it is an object of this invention to provide a new hermetically sealed package for electronic devices, as for example semi-conductors, which is relatively low in cost.
It is another object of this invention to provide an improved hermetic sealing means from such containers having reliable hermetic sealing properties.
It is yet another object of this invention to provide a method of fabricating a hermetically sealed container for an electronic device as for example a semi conductor, and a method of fabricating hermetic sealing means for the cover.
Other objects will be apparent from the following description, taken in connection with the accompanying drawings.